1. Field of the Invention
The present invention is directed to a process for producing battery separators from nonwoven mats of thermoplastic fibers. More specifically, the present invention relates to nonwoven structures produced from a mat of randomly laid, self-bonded fibers, preferably polypropylene, polystyrene or mixtures thereof, which are wetted by a surfactant to modify the surface properties of the fibers in the nonwoven mat.
2. Prior Art
The currently commercially used battery separators are mainly of two types: (1) resin impregnated paper, and (2) microporous rubber. The most commonly used material in auto batteries is resin impregnated paper; however, this material is brittle and is more susceptible to acid deterioration than is desirable. The microporous rubber separators are also more brittle than is desired and are much more costly than the resin impregnated paper. The microporous rubber separators are used mostly in industrial battery applications.
Battery separators made from polyolefins, specifically polypropylene, are illustrated in the following patents:
U.S. 3,002,040 U.S. 3,092,438 U.S. 3,026,366 U.S. 3,216,864 U.S. 3,045,058 U.S. 3,314,821 U.S. 3,055,966 U.S. 3,351,495 U.S. 3,084,091 U.S. 3,354,247